Abstract: Evapotranspiration is an important part of water cycle, and the study of evapotranspiration is conducive to understanding the spatio-temporal variation of regional water resources. The Yellow River Basin (YRB) is located in an arid and semi-arid region, and water resources are sparse and uneven in spatio-temporal distribution, and the water issues are prominent. Analyzing the response of evapotranspiration to the changing environment in the YRB and revealing the hydrologic and water resources effects of climate change, vegetation seasonality and phenological variations are of great theoretical and practical significance for the sustainable development and planning and management of regional water resources. Based on the Multivariate Adaptive Regression Splines(MARS) non-parametric model, this paper analyzes the correlation between the water-energy coupling control parameter ϖ and environmental variables under the Budyko framework by using the third generation normalized differential vegetation index datasets(NDVI_3g) developed by Global Inventory Modelling and Mapping Studies, meteorological data, soil data, land use/cover data and topographic and geomorphic data of 30 sub-basins in the YRB. The influence mechanism of changing environmental variables on evapotranspiration is discussed. The results show that (1) the spatial variation of the water balance relationship is significantly correlated with the water-energy coupling seasonality, the spatial variability of geomorphology, and the precipitation seasonality (average storm depth and coefficient of variation of precipitation). (2) On the inter-annual scale, a) the water and energy synchronicity is the most important climate seasonality that affects the inter-annual water balance: as water and energy synchronicity increases, the evapotranspiration ratio decreases and runoff yield increases; b) the more concentrated the precipitation, the higher the annual variation and the more obvious the seasonal precipitation, suggesting the smaller the evapotranspiration ratio; c) vegetation seasonality is an important factor affecting the catchment water balance: the stronger the vegetation growth and the longer the growing season, suggesting the larger the evapotranspiration ratio and the smaller the runoff yield coefficient. (3) There is a strong auto-correlation among environmental variables, which co-evolve and act on evapotranspiration.